You could call ddrescue with the parameter --max-size=1T (or whatever
the precise value is) to limit it to the first 1 TB.

What surprises me is that your drive is recognized as bigger than it
should be. I've heard of manufacturers limiting the size via firmware
settings for sales reasons, but limiting it to half the capacity?
Anyway, I'd recommend you find out why the reported capacity is twice as
high as it should be and more importantly that the data you copy using
ddrescue is actually valid.